The present exemplary embodiment relates to optical grating assemblies. It finds particular application in conjunction with an assembly and method for an elastomer-based grating assembly based on a travelling surface relief pattern for use as a variable optical attenuator, and will be described with particular reference thereto. However, it is to be appreciated that the present exemplary embodiment is also amenable to other like applications.
Fiber networks normally employ point-to-point links, which are static, where most of the intelligence, provisioning and grooming functions are provided by electronics at the ends of each link. As network architectures grow in size and complexity, however, this approach to building and maintaining network infrastructure will not satisfy the requirements of reliability, efficiency and cost-effectiveness required by service providers. Therefore, the industry is moving to optically reconfigurable networks where optical paths, wavelengths and data rates are dynamically changed to satisfy network system requirements, such as provisioning new wavelengths, balancing data loads and restoring after-service malfunctions.
Variable optical attenuators (VOA) are used to permit dynamic control of optical power levels throughout a communications, telecommunications or other transmission network. As traffic in networks increase, VOAs may be used to dynamically lower the optical power levels depending on the length of the network route so that appropriate power levels are received at the end receivers. As an example of their usefulness, if a network is providing a wavelength route that is approximately 60 km in length, at a predetermined power, and the network attempts to change the wavelength route to one which is 30 km, it would be expected that excessive power would be delivered to the end receivers of the 30 km route, potentially resulting in a malfunction in the network. A VOA will lower the power output of the switched wavelength to permit a signal of acceptable strength at the end receiver. The VOAs may be maintained at a particular power level for long durations, e.g., several months or even several years. Drift of the output power of the VOA can become an issue under such circumstances.
Existing VOAs commonly implement mechanical systems to attenuate the light. In one design, attenuation is accomplished by moving two separate optical fibers, and in another by inserting a motor-driven blade or filter in the light path. While these devices have acceptable optical performance, tradeoffs include slow speed, undesirable noise and a potential for mechanical failure.
Work on a traveling wave concept has primarily been focused in the area of surface acoustic waves, piezoelectrics, and electro-optic modulators where refractive index is changed by the application of electric fields.
In one particular example, U.S. Pat. No. 6,556,727 to Minakata et al. in its Abstract describes the concept of a traveling wave-type optical modulator having a substrate made of an electro-optic material, optical waveguides fabricated on the top surface of the substrate, and electrodes for modulating an optical wave through the optical waveguide. The substrate is partially thinned from the bottom surface of the substrate to form a first thin portion and a second thin portion so the thickness of the first thin portion is set to be larger than the thickness of the second thin portion, and the optical waveguide is positioned in the first thin portion. Among other concepts, this application does not discuss the use of a traveling wave used to create phase gratings that have corrugations with nearly constant pitch and depth.
The foregoing material does not address the noted shortcomings of existing systems.